Magnetic resonance imaging and ultrasonography in predicting pathologic extent after preoperative chemotherapy in stage II-III breast cancer

Introduction and aims: the main advantage of preoperative chemotherapy (PCT) is tumor down-staging, that can allow either mastectomy in large, inoperable primaries, or breast conserving surgery (BCS) for patients initially candidate to mastectomy. Therefore, an accurate measurement of residual disease after PCT is critical in the optimal surgical planning. Aim of this study is to evaluate the accuracy of breast magnetic resonance imaging (MRI) and ultrasonography (USG) in predicting the extent of breast residual disease. Patients and Methods: patients with stage II-III invasive breast tumor receiving PST and imaged with post-treatment MRI, USG or both were included; deltas were calculated as differences between the longest tumor diameter as measured by MRI and USG and the pathologic size of residual breast tumor. Differences between deltas were tested by using T test for paired data. Results: 45 patients treated with PCT in our Institution were eligible. Patients characteristics were as follows: mean age 50 yrs (range 30-70 yrs); stage IIA 31%, IIB 49%, IIIA-B: 20%. Eighty-nine % of the cases had ductal histology, 69% had ER positivity, and 24% had HER2 over-expression. The mean T size at diagnosis was 3.8 cm (range 1.5-8 cm). PCT type was anthracycline-based (24%) or anthracycline-taxane combination (76%). Forty-four patients have been evaluated after PCT by MRI, 41 by USG, 40 patients by both MRI and USG. The mean T size (range) after PCT was 2 cm (0-6.5 cm) and 1.7cm (0-5cm) as measured by MRI and USG respectively. The mean interval between breast imaging and surgery was 20 days (range 1-63). Type of surgery was mastectomy in 45% and BCS in 55% of the cases; 6 patients (13%) achieved a pathologic complete response (pCR). The mean pathologic T size was 1.98 cm (range 0-6 cm). The mean of the deltas were 0.04 (SD 1.91) and -0.19 (SD 1.53) for MRI and USG respectively (p=0.22). A complete response by MRI was observed in 9 cases: 3 cases were confirmed as pCRs; 2 cases presented with scattered microscopic residual disease. An USG complete response was observed in 8 cases (4 confirmed pCRs). Conclusion: in this series of patients, MRI and USG do not show significant differences in predicting the breast residual tumor after PCT. The major challenge for breast imaging after PCT is represented by scattered residual disease